Various manufacturing processes require controlled heating or cooling of components conveyed through a chamber with the intent of achieving a uniform temperature profile along the components. An example of such a process is the production of thin film photovoltaic (PV) modules (“panels”) wherein individual glass substrates are conveyed linearly through a pre-heat stage prior to deposition of a thin film layer of a photo-reactive material onto the surface of the substrates. It is important to obtain uniform heating of the substrates prior to the deposition process. Non-uniform heating leads to processing problems, such as bowing of the substrates, non-uniform deposition of the film layer, inconsistent film performance properties, and the like, all of which adversely affect overall performance of the PV module.
A continuous linear flow of discrete substrates through a steady-state heating or cooling chamber is prone to producing temperature non-uniformities in the components. Such non-uniformities may be the result of a combination of factors, including gaps or spaces that exist between the components, moving the components past stationary heating or cooling elements, and non-uniform conveyance rates of the components. With respect to gaps between the components, because the edges of the components have a greater surface area as compared to the interior or center region of the component, the edge regions have a reduced thermal mass and will heat or cool quicker as they are conveyed past a steady-state heating or cooling element. Conventional steady-state heating or cooling chambers do not adequately compensate for these edge-induced temperature irregularities.
Another potential cause of temperature variances along the substrates is that, in certain systems, the substrates are rapidly conveyed into the heating chamber such that a negligible time differential is created between when the leading and trailing edges of the substrates begin to be heated. Thereafter, the substrates are conveyed at a relatively constant speed through the chamber. This results in an increasing temperature gradient along the length of the substrate as the substrate moves linearly out of the heat zone because the trailing edge portions remain in the heat zone longer than the leading edge portions.
Accordingly, there exists an ongoing need in the industry for an improved system and method for the uniform heating or cooling of discrete, linearly conveyed components, especially glass substrates conveyed through heating or cooling chambers during the production of PV modules.